Do not flush this down the toilet!

The toilet may be inside the house, but it directs everything that is disposed in it, eventually, into the environment. Therefore, the toilet is not part of the municipal waste collection system.

Scientists from the Research Institute for Water and Waste Management (FiW) have investigated what happens to municipal wastewater flows in the basins of sewage treatment plants. More precisely, they focused on what should not be there.

The objects of interest were plastic residues. The researchers looked for the smallest particles (1-5 mm) as well as larger plastic fragments. The study was carried out in municipalities in the Aachen area. Not only wastewater flows were recorded, but also precipitation runoff on traffic routes, which, given sufficient rainfall volume carries away everything that lies on the road. It’s where a lot of rubbish ends up.

What the experts discovered as part of the "InRePlast" project funded by the Federal Ministry of Education and Research is thought-provoking, but not surprising: cigarette filters accounted for between new and 28 per cent of the waste, topping the list of the top 5 polymer finds. This was followed by polymer-based residues from hygiene products as well as tampon and sanitary pad packaging and cotton buds. The number of wet wipes, disinfectant wipes and kitchen paper residues was also considerable. But all this should not be flushed down in the toilet, complains Dr. Marco Breitbarth from FiW, not least because, depending on the weather, considerable amounts of wastewater from the public sewage system do not even arrive at the treatment plant.

During heavy rains, wastewater flows are sometimes diverted into overflow basins, which, when their capacity limits are exceeded, untreated wastewater is unceremoniously discharged into the surrounding water bodies. This means that packaging and plastic products disposed of carelessly and in the wrong place become an environmental problem.

According to estimates by the Federal Environment Agency (UBA), the discharge from the combined sewer system in Germany that is not treated in sewage treatment plants reaches an annual volume of around 1.3 billion cubic metres, while the discharge of precipitation water, which is also not covered by sewage treatment plants, amounts to a volume of just under 4 billion cubic metres. In contrast, about 10 billion cubic metres of wastewater were collected by sewage treatment plants. Around half of the wastewater treated by sewage treatment plants seeps into the environment uncontrolled - and leaves clear traces.

However, it is not only consumers who need to rethink and change their behaviour in dealing with residues from daily consumption and toilet flushing. The solution to the problem can only be found holistically, i.e. if all parts of society join in. In this context, industry is also called upon to be more mindful in its use of raw materials. The researchers also found plastic pellets in three of the four sewage treatment plants examined. In some cases, pellets were even found on roadsides, reports project leader Breitbarth. The construction industry, too, needs to be more careful when dealing with insulation materials such as Styrofoam, whose finely crumbled fragments are dispersed by the wind in all directions.